The present invention relates to a projection image display apparatus for enlarging/projecting an image outputted from an image generating source, for example, a projection TV by a projection lens onto a screen, and a projection optical system employed in this projection image display apparatus. More specifically, the present invention is directed to such a projection image display apparatus suitable for increasing a color purity, and further for improving focus performance and contrast without deteriorating brightness of an image.
While various image sources are required, rear projection image display apparatus have been widely marketed as large screen projection optical apparatus in view of light weight, low cost, and compactness needs.
Within a cabinet of this rear projection image display apparatus, there are provided three projection tubes and projection lenses corresponding to the respective projection tubes. These three projection tubes independently produces red, green, blue-colored image light, respectively, as an image generating source (will be referred to as "red, green, blue image light projection tubes" hereinafter). Then, original images displayed on fluorescent planes, or fluorescent faces of the respective red, green, blue image light projection tubes are enlarged/projected onto a screen by the projection lenses so as to be synthesized with each other, so that a full color image may be displayed.
This rear projection image display apparatus is disclosed in, for instance, JP-A-3-224384, and employs a colored lens element in order to give the wavelength selecting characteristic (filtering effect) to the projection lens used in the green image light projection tube. This display apparatus uses the colored lens element to reduce a spurious component close to the red and blue wavelengths involved in the light emission spectrum of the fluorescent substance of the green fluorescent plane. As a result, the color reproduction range of the enlarged image displayed on the screen is expanded, the color aberration is reduced, and the focus performance is improved. Furthermore, the concave lens element located near the fluorescent plane of the projection tube is colored, so that the unnecessary light component which is reflected on the light projection (emission) plane thereof and then is returned to the fluorescent plane can be absorbed/reduced two times. Accordingly, the contrast performance can also be improved.
In addition, very recently, as described above, in order that the projection lens employed in the red image light projection tube other than the projection lens employed in the green image light projection tube is equipped with the wavelength selecting characteristic (filtering effect), the colored lens element is employed in the rear projection image display apparatus. This colored lens element causes the spurious component close to the green wavelength involved in the light emission spectrum of the fluorescent substance of the red fluorescent plane, to be reduced, so that the color reproduction range of the enlarged image displayed on the screen can be expanded. Similar to the green image light projection tube, since the concave lens element located close to the fluorescent plane of this red image light projection tube is colored, the contrast performance can also be improved at the same time.